In the related art, there exist positioning systems using received signal strength indications (RSSIs). Technology is known in which, when positioning, radio waves from three access points, for example, are received by a device to acquire RSSIs, and a location is estimated by trilateration on the basis of the acquired RSSIs.
Also, in the related art, there exists technology in which antennas are respectively disposed at one part and another part of the chassis such that high antenna emission characteristics are ensured irrespective of which part of the device the user is holding, and technology that calculates several provisional predicted locations by using the multiple calculation methods of triangulation, k-nearest neighbor, and minimum-perimeter polygon algorithms (see Japanese Laid-open Patent Publication No. 2004-179995 and Japanese Laid-open Patent Publication No. 2004-215258, for example).
Also, in the related art, there exists technology in which many radio tags are dispersed and which estimates the present location of a mobile device subjected to positioning by communicating with a plurality of radio tags, and technology that monitors communication conditions with a wireless base station, and in the case of detecting irregular interference, uses the variation in communication conditions to estimate the distance between a device and a wireless base station in a state without interference (see Japanese Laid-open Patent Publication No. 2010-175374 and Japanese Laid-open Patent Publication No. 2009-200926, for example).
Furthermore, in the related art, technology is known in which the propagation delay time and received signal strength indication of a wireless signal is computed and which detects the presence of any moving bodies between a base station device and a rangefinder device or another base station device. Technology is also known in which a body's orientation is determined according to a match or mismatch of antenna polarizations (see Japanese Laid-open Patent Publication No. 2010-223593 and Japanese Laid-open Patent Publication No. 2009-250661, for example).
Meanwhile, in the case of conducting trilateration, more suitable trilateration may not be achieved because of variations in received signal strength indication due to how a device or other information processing apparatus is held. Herein, the received signal strength indication (RSSI) from an access point to a device separated by a communication distance d may be computed with the following Equation (1).RSSI=Ptx+Gtx−Loss—d+Grx  (1)
In Equation (1) above, Ptx represents the transmitting power of the access point, Gtx represents the transmitting antenna gain of the access point, Loss_d represents the spatial loss over the communication distance d, and Grx represents the receiving antenna gain at the device. Also, the transmitting power Ptx and the transmitting antenna gain Gtx are parameters specific to the access point, the spatial loss Loss_d is a parameter determined by the distance, and the receiving antenna gain Grx is a parameter specific to the device (information processing apparatus).
In other words, by acquiring an RSSI, the device substitutes the acquired RSSI, the transmitting power Ptx, the transmitting antenna gain Gtx, and the receiving antenna gain Grx into the above Equation (1) to compute the spatial loss Loss_d. The device also acquires the distance to that access point according to the value of the computed spatial loss Loss_d. The device also conducts positioning of the device itself by acquiring the distance as above from three different access points.
However, the receiving antenna gain Grx described above varies according to factors such as the level of contact with a body or other dielectric body, for example. As the receive antenna included in the device nears a body, its antenna gain (directionality, etc.) worsens. Antenna gain also varies according to the level of contact with a body, worsening as the level of contact increases. Furthermore, a suitable distance may not be produced if the antenna gain is distorted.
Japanese Laid-open Patent Publication Nos. 2004-179995, 2004-215258, 2010-175374, 2009-200926, 2010-223593, and 2009-250661 are examples of related arts.